NASA To Explore Secret Layer Of Sun

09-10-2008

Space Daily





Next April, for a grand total of 8 minutes, NASA astronomers are

going to glimpse a secret layer of the sun. Researchers call it "the

transition region." It is a place in the sun's atmosphere, about 5000

km above the stellar surface, where magnetic fields overwhelm the

pressure of matter and seize control of the sun's gases.



It's where solar flares explode, where coronal mass ejections begin

their journey to Earth, where the solar wind is mysteriously

accelerated to a million mph.



It is, in short, the birthplace of space weather. Researchers hope it

is about to yield its secrets.



"Early next year, we're going to launch an experimental telescope

that can measure vector magnetic fields in the transition region,"

explains Jonathan Cirtain of the Marshall Space Flight Center (MSFC).

Previous studies have measured these fields above and below the

transition region-but never inside it. "We hope to be the first."



The name of the telescope is SUMI, short for Solar Ultraviolet

Magnetograph Investigation. It was developed by astronomers and

engineers at the MSFC and is currently scheduled for launch from

White Sands, New Mexico, in April 2009.



SUMI works by means of "Zeeman splitting." Dutch physicist Pieter

Zeeman discovered the effect in the 19th century. When a glass tube

filled with incandescent gas is dipped into a magnetic field,

spectral lines emitted by the gas get split into two slightly

different colors-the stronger the field, the bigger the splitting.

The same thing happens on the sun.



By measuring the gap, astronomers estimate the strength of the

sunspot's magnetic field. Furthermore, by measuring the polarization

of the split line, astronomers can figure out the direction of the

magnetic field. Strength + direction = everything you ever wanted to

know about a magnetic field!



This trick has been applied to thousands of sunspots on the solar

surface, but never to the transition region just a short distance

above.



Why not?



"Just bad luck, really," says Cirtain. "Gas in the transition region

doesn't produce many strong spectral lines that we can see at visible

wavelengths." It does, however, produce lines at UV wavelengths

invisible from Earth's surface.



"That's why we have to leave Earth."



SUMI will blast off inside the nose cone of a Black Brant rocket on a

sub-orbital flight that takes it to an altitude of 300 km. "We'll be

above more than 99.99% of Earth's atmosphere," says Cirtain. About 68

seconds into the flight, payload doors will open, affording SUMI a

crystal-clear view of the UV sun. "From that moment, we've only got 8

minutes to work with. We'll target an active region and start taking

data."



SUMI's "vector magnetograph" is tuned to study a pair of spectral

lines: one from triply-ionized carbon (CIV) at 155 nanometers and a

second from singly-ionized magnesium (MgII) at 280

nanometers. "There's nothing special about those ions," notes

Cirtain. "They just happen to produce the best and brightest lines at

temperatures and densities typical of the transition region."



Cirtain anticipates how it will feel to have his precious instrument

hurtling 300 km above Earth at 5,000 mph: "Eight minutes of terror."

He'll start breathing again when the payload doors close and SUMI

begins its descent back to Earth. Cirtain ticks off the

stages: "Reentry into the atmosphere. Open parachutes. Landing back

at White Sands. Recovery."



The short flight probably won't lead to immediate breakthroughs. "But

it will demonstrate the SUMI concept and show us if it's going to

work." A successful flight would lead to more flights and eventually

to a SUMI-style magnetograph permanently installed on a space

telescope.



"That's the dream," he says. Transition region, prepare to yield...

The glory of science is, that it is freeing the soul – breaking the mental

Manacles – getting the brain out of bondage – giving courage to

thought – filling the world with mercy, justice and joy.